One of the best sources of zinc is possibly Zincum Gluconicum. The form that clearly appears to be the most effective is as a nasal gel as found in Zicam's Cold remedies. The Zincum Gluconicum found in lozenges, such as Cold-Eeze, do not appear to be as effective as in the nasal gel product.

Note that Zincum Gluconicum has been found to be very effective against the common cold but might not do much for the flu. Its effectiveness has been reported in the prestigious QJM. The study can be found on PubMed.gov, a service of the U.S. National Library of Medicine and the National Institutes of Health. The abstract can be found at the NCBI (National Center for Biotechnology Information) web site: